The investigator proposes to continue study of the factors which regulate transport and urinary excretion of magnesium and the role of calcium in hormonal action. Microperfusion of isolated tubular segments will be utilized to determine mechanisms of transport and the effects of diet and hormones. Studies will be continued using electron probe microanalysis and NMR to characterize intracelluar phosphate concentrations and the relationship between this and the cellular effects of parathyroid hormone.